You can felt in the tub or sink, although a sink would be easier if the project isn't too large.
Fill your sink with hot water (hottest you can stand without burning yourself, you'll need to submerge your hands). Add a little bit of detergent. Then get aggressive on that knitting. Rub and agitate it as much as you can, but do not wring or twist it. Squeeze out the water, then rinse with cold water. Repeat until you reach the desired size and shape.